The present invention relates to a method and apparatus of manufacturing accreted filter cartridges or other accreted tubular articles and, particularly, to a method and apparatus for progressively forming cartridge elements of bonded fibrous material which are rigid, self-supporting and porous.
In general, the conventional process for forming accreted filter cartridges followed the process disclosed in U.S. Pat. No. 2,539,768 (Anderson). Recently, in Sicard, U.S. Pat. No. 3,995,076, a method for progressively forming a fiber batt was disclosed. In this patent, accretion, consolidation and dewatering of the batt occurred under a single constant vacuum condition. A standpipe, closed at its upper end was vertically mounted in a vessel designed to hold a quantity of fiber slurry. The lower end of the stand pipe was connected to vacuum source such as a pump. The standpipe was formed with a single, perforated section, along its length, above and below the level of the slurry. This porous section was defined by flexible seals at its upper and lower edges. A cylindrical mandrel was coaxially placed over the standpipe and it was moved upwardly along the standpipe, cooperated with the seal rings to form an internal vacuum zone. Because the vacuum zone extended simultaneously below and above the slurry level, as the mandrel was raised, the fibers could be progressively accreted, consolidated and dewatered.
This process, while producing an excellent filter cartridge, has several disadvantages. One is the necessity of a reciprocating movement to lower the close fitting mandrel over the standpipe and then to raise it from the standpipe during the accretion, consolidation and de-watering cycle. Since the standpipe is fixed only at the bottom of the tank a very rigid and precise, and therefore expensive, mechanism is required to lower the mandrel over the standpipe to almost the bottom of the tank. To obtain this rigidity, a relatively large reciprocating mechanism is required as well as a relatively large tank to receive the mechanism. This large tank, of course, requires a large amount of slurry which must be kept agitated at all times. This is accomplished by the use of a large agitator located in the bottom of the tank or by a large flow of slurry directed against the bottom of the tank to establish upward circulation of the slurry towards the top of the tank where the vacuum induced felting takes place. Since the standpipe and vacuum station is in the center of the tank which is approximately 30" square most of the slurry rising along the perimeter areas of the tank only overflows back to the slurry pump for recirculation. From an energy standpoint, this is a very inefficient "brute force" approach. It requires a larger recirculation pump as well as a larger vacuum pump as fiber content seldom exceeds 1.0% (dry weight).
The high recirculation rate of the fiber slurry through the pump causes fiber abrasion and reduction in both fiber length and diameter and consequently on the filtration integrity of the finished filter. Also, the vertical fiber movement must be overcome by the vacuum pump suction before the fibers can be sucked onto the felting mandrel. This requires either a larger vacuum pump or larger felting time. Another factor governing overall cycle time is the need to insert the new mandrel gently over the standpipe to prevent damage to either part. This requires at least 50% of the time required for the upward filter forming stroke.
Another serious disadvantage of the prior art is caused by the physical dimensions of standard filter cartridges. These are roughly 1.065" I.D..times.2.625" O.D..times.multiples of 10" long up to a maximum of 40". Under these conditions, the I.D. of the standpipe is limited to about 0.8" which will handle a water flow sufficient to felt a cartridge in a reasonable length of time. However, when a mixed two phase flow (liquid and air) as in the prior art must be handled in this cross section, felting time will increase regardless of the vacuum pump size.
It is an object of the present invention to overcome the disadvantages of the prior art devices and, in particular, to eliminate the need to reciprocate the mandrel in the slurry bath thereby eliminating the large slurry tank and accompanying large recirculation pump or slurry agitator, whereby construction and operating costs are greatly reduced.
It is a further object of the present invention to provide a method and apparatus where accreted batts can be formed in an inline unidirectional process, without the need for reciprocal mandrel loading movement, thereby the process is simplified and the speed of production increased.
It is a further object of this invention to provide a method and apparatus wherein the accretion portion of the process and the subsequent consolidation and dewatering steps are physically separate and independent, each being subject to its own vacuum source. This results in significantly less vacuum power use and loss, overall, permits faster processing and ends in significant economic advantage.
The foregoing objects and advantages, as well as others, will become more apparent from the following disclosure of the present invention.